The present invention relates to a collet, and more particularly to an improved collet having optimized parameters to maximize gripping strength, and a method for making same.
U.S. Pat. No. 2,346,706 to Stoner and assigned to the Jacobs Manufacturing Company describes a collet having a plurality of flat-sided gripping members. The gripping members are held in relative position equally spaced about a common axis. The spaces between the gripping members are filled with an adherent resilient material, such as rubber or rubber composition. The gripping members are also transversely perforated. In this case, the resilient rubber material not only fills the space between adjacent gripping members, but it also passes through the perforations in the gripping members thereby forming a plurality of longitudinally spaced continuous annular rings which hold the gripping members in desired relative positions. This collet was a significant improvement over the conventional split steel collets and is widely recognized today by those skilled in the art and commonly known as the Rubber-Flex.RTM. collet.
However, prior to applicant's present invention, it was not known to optimize the gripping strength of the Rubber-Flex.RTM. collet by determining optimum design parameters for the gripping blades or "jaws." Although a number of jaws having varying thicknesses were utilized in the collets, it was not commonly believed that gripping strength could be maximized by deducing the optimum number of gripping jaws for a given configuration which would fit around the inner diameter of the collet while maintaining at least a minimum amount of the resilient material between the gripping jaws. Additionally, the thickness of the gripping jaws was generally not considered as effecting gripping strength. Typically, the jaw thickness was dictated by the size or inside diameter of the collet. In other words, smaller diameter collets had thinner jaw blades.
U.S. Pat. No. 5,123,663 to Mizoguchi discloses a method for determining the minimum number of segments for a metal collet by determining the range of a central angle (theta) where the geometrical moment of inertia for each segment is constant with respect to a line passing through the centroid of the section perpendicular to a radial direction of the collet. The patent discloses that the range of angle theta is less than 30.degree. regardless of the thickness of the segment. Once the central angle of about 30.degree. is attained, any further increase in the number of segments will only increase the number of manufacturing steps and lower the tensile strength a cylindrical portion of the collet.